NanoVNA – the £30 handheld 900 MHz VNA
Update Nov 2019 £47 – NanoVNA’s are now available on Ebay for as little as £29.75!! At this price they don’t include SMA cables but you can buy better quality cables made with RG316 for £2.42 each on Ebay. All prices include shipping from UK sources.
Why do you need a VNA? Simply put they’re a far better way of checking antenna tuning than using an SWR meter or a regular antenna tester and can generally be used to test filters and other components. Two or more plots can be displayed simultaneously, with Smith chart and SWR being a useful combination for antenna testing.
The club has a little Sark 110 VNA handheld, which has an LCD screen that lets you see exactly what your antennas are up to. These are great little devices, covering up to 230 MHZ but they cost £330, so not an impulse buy.
Enter the NanoVNA, a handheld VNA with a 2.8″ touchscreen and a frequency range allegedly extending up to 900 MHz. It appears to be possible to use it as a CW signal generator too (although it almost certainly generates square waves). You can also connect it to a PC by USB and a simple programme lets you control it and see plots on the PC screen. NanoVNA Saver, is a better and open-source solution written by Danish ham Rune Broberg. It has many additional features including more data points and a Time Domain Reflectometer function that tells you how far away the damage is when your feeder goes high SWR.
NanoVNAs generally come with a basic SMA calibration set consisting of an open circuit, a short circuit, a 50 ohm load, a pair of cables and an F-F back to back adapter. These are essential as the VNA only produces sensible readings if calibrated for the frequencies under test. The calibration process is quick and easy. The NanoVNA feature set probably isn’t as wide as a more expensive VNA but at this price you are already getting more than you can reasonably expect.
The design started off as an open source project on Github but a number of Chinese manufacturers have started making them and selling via Ebay and other online marketplaces. There are variations between these clones and it is difficult to know which one you will receive when you order as they may ship a different version to that shown in the ad. The better versions have screening round the input and output circuitry. Some people buying via Chinese sites like Alibaba find the device ships without a battery due to postal restrictions. There are also several different versions of firmware – some make it a 4-trace 2-port VNA. Others a 2-trace 2-port antenna analyser with a clearer display.
Although the NanoVNA is usable out of the box it is all a bit DIY – it doesn’t come with a case or with a manual. You can find a basic ‘Chinglish’ manual online as well as a useful forum, stl files for 3D cases and firmware. The firmware is basic but does the job. Some people find there are glitches at 300 and 600 MHz so some firmware variants go to 800MHz max to avoid this.
I bought a NanoVNA from ‘UK’ seller sqcase. It looks slightly different to what was advertised, isn’t the best version and the firmware is for an antenna analyser (which means it has a larger font and only displays two charts at a time) but it came quickly with a battery and no customs charges. It seems to work remarkably well for what is essentially a giveaway price. Unfortunately the SMA short circuit was missing from my calibration set and the seller unresponsive. Easy enough to make a shorted SMA as long as you have a spare plug – shame the Maplin stores all closed! Homebrew shorts don’t work as well at higher frequencies though, so I had to get a better one to benefit from the full frequency range.
Here’s what mine looks like, displaying the Smith chart and SWR plot for a 2m/70cm handheld antenna. Note the rather fetching red case, printed with my Anycubic Mega 3D printer from a design on Thingiverse by VK5ZBR. I had to increase the size of the case fractionally and do a little filing as it was designed for a different clone but it is a snug fit and doesn’t need any glue or fixings:
My NanoVNA seems to work ok all the way up to 900 MHz, at least now I have a proper calibration set. Not only is it useful for measuring antennas it can also be used to test filters by connecting them between the two ports and changing the diaplay so it shows the signal from the second port.
You can buy a NanoVNA by searching Ebay and there’s a helpful user group here: https://groups.io/g/nanovna-users astonishingly there are a number of VNA experts on the group and they’ve been stunned at how well results the NanoVNA compares with their ‘big brand’ VNAs.
The io group also has a wiki that includes instructions and links to various new firmware versions, including one that extends the measurement range as far as 1500 MHz. (The performance drops off significantly but it is probably ok for measuring the SWR of antennas for the 23cm band.)